With requirement for miniaturization of electronic components, in a circuit module in which semiconductor integrated circuits and circuit components are installed, it is necessary to install a large number of semiconductor circuit chips and circuit components and a demand for effective utilization of a wiring space and a mount space grows.
Particularly, a signal used in an optical communication field is a digital signal and thus an analog signal connected to output of a light reception element and a digital circuit installed for the purpose of for synchronizing a reception signal, etc., are mixed. Thus, there is a problem in that noise occurring in the digital circuit invites characteristic degradation of the analog circuit and hitherto various measures have been considered.
As an example, a structure wherein an analog circuit is placed on one face and a digital circuit is placed on an opposite face across a grounded conductor plate is proposed (Patent Document 1).
According to the configuration, electromagnetic wave noise caused by the digital circuit is blocked by the conductor plate and does not arrive at the analog circuit and thus noise can be decreased. The device can be miniaturized because of double-face mounting configuration.
The applicant proposes various structures such as a structure wherein the area of bypass capacitor power supply wiring is made narrow so that a high frequency current occurring from an IC power supply terminal does not pass through a bypass capacitor and a power supply pattern for an IC power supply terminal and a power supply pattern for external power supply are spatially separately provided in a multilayer circuit board which easily becomes a generation source of unnecessary radiation noise (Patent Document 2).
Particularly, in a modulation/demodulation IC for modulating and demodulating, a large number of ground terminals (pads) are placed at narrow pitches and are connected onto a mount board. As the mount board, a stack board with a plurality of wiring layers stacked through an insulating layer is used (Patent Document 3).
In such a stack board, to lessen routing of wiring as much as possible and decrease impedance caused by the wiring, usually a power supply line and a ground line of the wiring layers are formed each in a plate and are embedded in the stack board as a power supply plate and a ground plate.
In an electronic device often involving mounting of a high heat generating component of an amplifier, etc., various radiation structures are proposed and a structure wherein a base board such as a metal base board is caused to radiate is proposed (for example, Patent Document 4).
Patent Document 1: JP-A-1992-252624/1992
Patent Document 2: JP-A-2003-297963
Patent Document 3: JP-B-3375555
Patent Document 4: JP-A-2006-135202